I have to agree with the others. The Phillipines were a McArthur plan to save face, as he had promised that, "I shall return." There were Navy plans to bypass the Phillipines and invade Formosa - it would have made Okinawa and Iwo Jima look like neighborhood brawls, by comparison. Why invade Formosa? To cut off Japanese raw materials from their new colonies in East Indies. As it turned out the US "Silent Service" cut the supply line for a much lower cost than invading either the Phillipines or Formosa. Now the Philipines were a US 'Colony" and Philipinos had fought very well as part of the US and Phillkipine armies in initial defense - a political reason to invade.

As far as Iwo Jima - it was needed as a fighter base to escort B-29s to Japan and as an emergency field between the Marianas and Japan. The first damaged B-29 landed there while the Marines were still cleaning out the Japanese.

That my $.02

Why, in 1944 after the Marianas campaign, did the U.S. invade the Philippines to the South instead of continuing North East toward Iwo Jima and eventually the Japanese home islands?

The lives of many of the former Bataan defenders were saved by the invasion. If the island was bypassed, many more of the prisoners-of-war would have perished. As it was, many were just abandoned in their remote jungle prisons by their Japanese captors. If the island was cut off from resupply, the Japanese may have just executed the prisoners or let them starve to death.

The Central Paciifc theater, under ADM Nimitz was still progressing along their island hopping campaign thru the Marianas then turning North towards Japan. Whether McArthur invaded the Phillipines or Formosa had no real affect on Central Pacific drive, although the Naval battles around the Philipines wouldn't have taken place.

OK, here's a 'what if.'

Why, in 1944 after the Marianas campaign, did the U.S. invade the Philippines to the South instead of continuing North East toward Iwo Jima and eventually the Japanese home islands?

The eight month delay in going after Iwo allowed the Japanese to build tremendous defenses and reinforce the island.

Now what's interesting here are not only the military questions but also the political ones; the relationship between the MacArthurs and the Roosevelts, the fact that it was an election year (yup, no assurances of who would be voted in or out), etc.

The Japanese Navy has said this was a big U.S. blunder. Certainly the Iwo campaign was bloody when it happened in '45. What was gained by invading the Philippines? What if they had been bypassed.

I take no responsibility for what happened either way. I ask not because I agree or disagree with what happened and therefore cannot be changed.

Steve

A battle in the Formosa straights would have had decent air cover from the surrounding Japanese territories. Kamakazes would have been there in numbers protecting the remnants of their fleet. The possible loss of US ships may have been much higher than they were.

US plans for an invasion of Formosa invisioned taking and holding the southern half of the island only. There were no decent harbor and deep water port facilities on the island and therefore plans to take and hold Amoy on the mainland were included. The problem here is that even if the plan works, the Japanese still hold the North half of the island with airfields and can move reenforcements at will onto the island. Additionally, they can easily reposition forces on the mainland to retake the port of Amoy which would leave the Allies without a supply route.
I don't think the decision to invade Formosa or The Phillipines was drawn along service lines (Army/Navy). Most of the Joint Chiefs, Nimitz and MacAurther agreed that the Southern portion (Leyte,Mindanao)of the Phillipines would have to be taken first. The question was, should the next move be Formosa or Luzon. One of the reasons the Phillipines were chosen is the fact that the allied knew they could count on the populace to support them.
Some actually advocated bypassing both and just assaulting Japan but logistics didn't support that idea.
Bottom line of my ramblings is that the way I see it, Iwo Jima wasn't really being discussed at this point ('43-'44) - the choices were Luzon or Formosa.

DJ,

I have found a lot of good info at the Center for Military History. Here is a link within that site to a good article with some insight on planning. https://www.army.mil/cmh-pg/brochures/luzon/72-28.htm ( I'm not sure if I got the hyperlink thing right - can you tell I'm not too comfortable with computers?) The writing can be a little dry, but there is less author opinion and more fact.
By the way, thanks for posing these questions. It's good to think outside the box now and then.
v/r,
Cob

don't want to get too parochial, but we are both US Army, and you are giving the Marines all the credit for Okinawa. The landing force, under command of 6th Army, consisted of 1st, 2nd, & 6th Marine Divisions, but also 7th, 96th, 27th, 77th & 81st Infantry Divisions. The preparatory securing of the Kerama Islands, for an achorage, was secured by an Army unit (77th Infantry Div), and the Okinawa assualt force consisted of two Marine and two Army Divisions

Sorry, had to vent. I've had to listen to too many people that don't even know that the Army was in the Pacific War, or that the Army's only participation was the loss of the Philipines and then the Marines saved the day. The US Army still has more wartime amphibious landings than the Marines

Next you'll claim that the Army has more ships than the Navy! :-)

Cob